1. Field of the Invention
The present invention relates to an electronic apparatus, such as a portable computer having a 180° rotatable display unit, and more specifically to a structure connecting the display unit to a main unit.
2. Description of the Related Art
For example, Japanese Patent Application KOKAI Publication No. 11-39058 discloses a notebook-type portable computer having a 180° rotatable display unit. The portable computer has a hinge mechanism connecting the display unit to a main unit. The hinge mechanism has a horizontal first shaft extending in the width direction of the main unit, and a vertical second shaft perpendicular to the first shaft.
The first shaft of the hinge mechanism connects the display unit to the main unit such that the display unit is rotatable between a closed position, where the display unit overlies the main unit, and an open position, where the display unit is raised up from the main unit. The second shaft of the hinge mechanism connects the display unit to the main unit such that the display unit is 180° rotatable in the circumferential direction of the second shaft.
With the above structure, the display unit can be rotated 180° about the second shaft in the state where the display unit is in the open position. As a result, the screen located on the front surface of the display unit is turned to the back of the main unit. Therefore, the screen can be observed from behind the main unit. When the display unit is rotated from the open position to the closed position in the state where the screen is directed to the back of the main unit, the display unit lies on the main unit and the screen is horizontal. In this state, the screen can be used as an input surface, so that various operation can be input by touching the input surface with a finger or a pen.
The hinge mechanism is located at a center along the width direction of the portable computer. With this structure, the main unit and the display unit are coupled at a single portion. Therefore, the torque that is produced when the display unit is rotated between the closed position and the open position and the torque that is produced when the display unit is 180° rotated about the second shaft are liable to concentrate at the centers of the main unit and the display unit.
In the portable computer, to maintain the display unit at an arbitrary open angle, braking force which limits free rotation of the display unit is exerted on the hinge mechanism. Therefore, when the display unit is rotated from the closed position to the open position and vice versa, high torque that can overcome the braking force is required. Accordingly, great stress is inevitably exerted on the connecting portion between the main unit and the display unit and the hinge mechanism. Therefore, high rigidness of the connecting portion and the hinge mechanism is required, and the size of the connecting portion and the hinge mechanism may be increased for this purpose.
As to recent portable computers, there is a demand for a thin and small main unit and display unit for convenience of portability. For this reason, since the connecting portion between the main unit and the display unit and the hinge mechanism cannot be excessively large-sized, sufficient rigidness of the connecting portion and the hinge mechanism cannot be maintained. Therefore, the display unit wobbles when it is rotated, resulting in low operability.